Unconventional hydrocarbons are hydrocarbons which come from subterranean rock formations, or reservoirs, that were previously deemed unproductive and uneconomic. Due to recent technological innovations and an abundant in-place supply, unconventional hydrocarbons have emerged as the potential energy resource of the future. Shale rock and/or tight rock are examples of an unconventional hydrocarbon source which is currently being exploited for the recovery of hydrocarbons as a reliable, affordable, energy source. The relatively large reserve of hydrocarbon resources trapped in shale rock formations has become more accessible over the past decade based on combining two established technologies: multistage hydraulic fracturing, and horizontal drilling. Historical processes to fracture rock include using dynamite, freezing, perforating explosives, pressurized water and other fluids, that can hydraulically fracture.
Hydraulic fracturing is a process used in most unconventional hydrocarbon wells. Large amounts of fracturing fluids including water, sand or proppants, and chemicals are pumped underground through a wellbore and delivered to a hydrocarbon-bearing subterranean rock formation to hydraulically break apart the rock for release of the hydrocarbons contained inside.
Typically, large hydraulic fracturing operations (also known as hydrofracking or “fracking”) break subterranean rock formations by using pressurized fluids to create pathways for hydrocarbons to flow to the wellbore. Post-treatment, the hydrocarbons are conducted to surface through the wellbore. Hydraulic fracturing, therefore, “stimulates” the reservoir by simply breaking the rock to increase the conductivity, or flow pathways, of the reservoir to the wellbore.
Current hydraulic fracturing technologies use large quantities of pressurized fluids, typically water, in order to effectively break the rock and stimulate the reservoir. Proponents of hydraulic fracturing point to the economic benefits of the vast amounts of formerly inaccessible hydrocarbon energy which the process can extract. Opponents point to potential environmental impacts, including consumption of large volumes of fresh water, risk of breakthrough to, and contamination of, ground water, and the hydraulic fracturing chemicals causing contamination. The finite supply of fresh water should be treated as a valuable resource, such as to be made available for human consumption, and not necessarily as merely a low cost consumable for hydraulically fracturing rock formations.
For these reasons hydraulic fracturing has come under scrutiny internationally, with some countries suspending or banning it. Technical tools such as fracture simulation models, casing and cement designs and micro seismic data demonstrate that hydraulic fracturing, when executed according to proper design, is not the primary way that surface and ground waters become contaminated. The high volume of fresh water usage for unconventional formation fracturing has yet to be addressed properly, and is the focus of this technology.
In unconventional hydrocarbon recovery, horizontal wells are drilled and completed with multistage fracturing in order to effectively yield more stimulated subterranean rock. Each well utilizes hydraulic fracturing of about 10-40 multistage, spaced completions along the wellbore, each stage requiring water volumes of about 50 m3 to 5000 m3 of water. Overall, the multistage technology works well. For water conservation purposes, water recycling technology is being investigated, but is certainly not in widespread use. Applicant understands that an estimated 20% of the water pumped down for hydraulic fracturing is being recovered yet there can be restrictions, cost and complications in the application and reuse thereof.
The unconventional fracturing fluid typically comprises a mixture or slurry of water, proppants, chemical additives, gels, foams, and/or compressed gases. Typically, the fracturing fluid is 98-99.5% water with the chemicals accounting to 2 to 0.5%. The sand proppants are most often quartz with a specific gravity of 2.65 g/cc. Fresh water is overwhelmingly the largest component of hydraulic fracturing in unconventional hydrocarbon reservoirs.
A hydraulic fracturing operation for a single unconventional shale well can consume an amount of water equivalent to supply a population of 4,000 people for a day. In addition to the large volumes consumed, large amounts of energy are required to transport and prepare the water. It is becoming more apparent that the cost of water in today's usage has not caught up to the value of water in tomorrow's world. It is arguable that the current hydraulic fracturing process is not environmentally sustainable long term.
A long standing problem for mankind has been the need for a constant supply of fresh water. Fresh water to sustain human, animal and plant life comprises approximately 1-3% of the water on earth, including rain water, rivers and streams, and ground water. The prolonged use of water volumes for hydraulic fracturing can impact vegetation, animal, and human life. The technology being implemented today to obtain the valuable unconventional hydrocarbon resource adds additional stress to the environment in a negative way, impacting everyday life.
Unconventional hydrocarbons are emerging as a significant economic energy resource for the future, however further production techniques require advances in technology to harvest the abundant supply. It is incumbent on the industry to find an alternative process that will break rock, will honor the water resources, will not harm the environment, and will be economically executable.
Accordingly, a need remains for a fracturing process method in order to overcome the above-noted shortcomings.